Electric motors are used in many applications, from electric fans to vehicle engines. However, electric motors may occasionally stall. For example, an electric motor can become stuck in a particular position or vibrate back and forth due to unexpected load conditions. The motor circuit (i.e. the circuit that drives and controls the motor) is tasked with detecting and correcting a motor stall condition. The first step in correcting a stall condition may be to detect the stall and generate an error.
Many motor circuits detect a motor stall by looking for a zero-crossing in the value of a back electromotive force (back-EMF) signal. If no zero-crossing occurs, it can indicate that the motor is stalled or stuck. However, this method cannot detect if a motor is wobbling back and forward with a certain frequency. Because the back-zero crossing occurs when the motor is vibrating back and forward, the controller often assumes the frequency at which the motor is vibrating is the actual rotational speed. Therefore, using this technology it may not be possible to detect a motor stall problem.